look on the label, i think it is fenbendazole but i'm not sure. I *think* it's pretty safe, but I'd recommend googling the "kill rate" or "kill ratio" i think it is called and you'll get the dose at which 50% of the animals in the test group died.skruck said:Hi, does anyone know if Safegaurd cattle wormer blocks will hurt my horse. She is really liking it and I don't know if I should let her have it.